The present application is related to, and hereby incorporates fully by reference the entire disclosure in U.S. patent application entitled “Integration of Thermally Conductive but Electrically Isolating Layers with Semiconductor Devices,” naming as inventor David J. Howard, and filed on the same day as the present application on Jun. 27, 2016, and having U.S. patent Ser. No. 15/194,183.
In monolithic radio frequency (“RF”) circuits, losses associated with the substrate impedance have deleterious effects on performance. For example, in RF switches built on bulk substrate technology with junction isolations, parasitic substrate impedance (e.g., capacitive coupling) can result in degraded linearity and voltage imbalance across large branches of stacked semiconductor devices. Other deleterious effects may include higher parasitic losses suffered by passive components (e.g., transmission lines, inductors, etc.) reflected in lower quality factor, and unwanted crosstalk between devices or circuit blocks through the substrate.
In monolithic RF circuits utilizing bulk substrate technology, propagation of signals in the substrate medium can introduce unwanted second and third harmonics, which can significantly degrade the linearity of the RF signals. Some of this degradation can be partially mitigated by using high resistivity substrates. In a conventional monolithic RF circuit employing a high resistivity substrate, fixed positive charges in the dielectric layers on top of the high resistivity substrate, can induce an inversion layer in the high resistivity substrate. For example, due to the low background doping of the high resistivity substrate, the fixed positive charges can cause an accumulation of high mobility carriers of opposite polarity under the dielectric layer. This inversion layer of high mobility carriers can significantly decrease the effective resistivity of the high resistivity substrate. In addition, the capacitive coupling between one or more of the metal layers and the high resistivity substrate can also become voltage dependent.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by substantially eliminating substrate parasitics and improving RF signal linearity of monolithically integrated RF circuits.